It is well known that the isochronism of a sprung-balance regulating device can be disrupted by variations in external conditions, such as the temperature and magnetic field. In order to compensate for, or reduce the influence of such variations, numerous solutions have been proposed and/or retained as regards the choice of materials, or forming of the balance and balance-spring.
As far as the balance-spring is concerned, the shaping of the inner curve for securing it to the balance staff, the shaping of the outer curve for securing it to the balance-cock, and the means implemented for carrying out said securing play a determining part as regards isochronism. The invention concerns more specifically the means for securing the outer curve to the balance-cock, directly or via a balance-spring stud, generally supported by a mobile balance-spring stud carrier for positioning the balance-spring.
The outer curve of the balance-spring is most often secured by pins or bonding, although other solutions have been proposed. It has, for example, been proposed to add an inertia-block, set in one edge of the balance-cock, to the end of the curve, as disclosed for example in U.S. Pat. No. 1,037,741, wherein the inertia-block has a triangular shape. Such a construction makes manufacture of the balance-spring more complicated, in order to form an inertia-block at one end and requires a particular arrangement of the balance-cock, different from the usual arrangement of the balance-cock stud.
The usual securing using pins or bonding has the drawback of not guaranteeing the positioning of the point of contraction/expansion of the balance-spring over time, either because of slight movement, or because of aging and/or the glue crumbling.